I have both S4 and X10. X10 is light years ahead of the S4 in accuracy, smoothness,balance and clarity.Vocals are more realistic and bass tighter and less muddy. If vocal clarity and mids are your thing there really is no hard decision between the two. The X10's are supremely comfy for anyone with very small ear canals, like me. Having said that, after experiencing my Senn IE8's i'll never appreciate either the way i used to. They make both put together sound like a dime store special once burned in, at least to my ears. Their soundstage,imaging, and tonal balance just push all the right buttons, but you'll still grin with the X10's.
